Research On Reliability Evaluation Of Deep Well Casing Column

The casing plays a role in protecting the wellbore,strengthening the wellbore,isolating the oil and gas layers,and sealing various complex formations during drilling and oil recovery,ensuring the normal operation of drilling,completion and oil production,and at the same time occupies the cost of well construction.High ratios,so the safety of the casing is very important.In the design of strength of casing string in deep wells,the environment and stress of the casing are relatively complex.However,the current considerations for the design criteria of the casing string are relatively simple.Therefore,in many cases,the safety of the designed casing is at risk.There are three main reasons for this problem:(1)Insufficient consideration of casing string loading and factors affecting casing strength;(2)No consideration of the randomness of casing string load and strength;(3)Due to safety factor The randomness,using it as an indicator to evaluate the safety of casing is not very reasonable.Therefore,this paper has done four aspects based on the current strength standard for casing string design.First,the air column pressure at high temperature and the outer squeeze force of the creep layer casing were studied,and the effective external load calculation method for casing string was established.Secondly,based on the uniaxial and triaxial stress of the casing,the impact of non-uniform external extrusion load on the casing's collapse strength was studied.It was found that the external extrusion strength of the casing was nonlinear as the non-uniform coefficient of the external load was reduced.Reduce;According to the "wear-efficiency" model,predict the amount of casing wear and study the residual strength of the casing after wear;study the influence of the temperature of the casing material on the strength of the casing and the human stress of the casing when there is a temperature difference.The residual strength of the casing under uniform corrosion and local corrosion is studied.When the corrosion depth is less than half the wall thickness,the effect of local corrosion on the impact strength of the casing is greater than the effect of uniform corrosion on the casing collapse strength;the corrosion depth is greater than When the wall thickness is half,the effect of local corrosion on the impact strength of the casing is less than the impact of uniform corrosion on the casing's impact strength;the strength of the casing after perforation is studied based on the knowledge of elastic mechanics,and the aperture,hole density and phase pair are analyzed.Effect of casing strength.Thirdly,according to interval mathematics theory,casing load and strength calculation method,the calculation method of casing load and strength interval is established,and the randomness of load and strength is analyzed.Based on the ellipsoid convex non-probabilistic reliability theory,a set of The ellipsoid convex non-probabilistic reliability model;the reliability of the casing is correlated with the safety factor,the relationship between the reliability and the safety factor is obtained,and the coefficient of variation of the load,the coefficient of variation of the strength,and the safety factor are studied.Impact.Finally,the software was tested with the DX well and the safety factor of the casing calculated by this method was lower than that calculated by the current standard,especially in the creep interval.The calculation results also show that when the safety factor is used to evaluate the safety of the casing,the requirements can be met.However,when evaluating the casing with reliability,the casing safety has risks.Therefore,the study of reliability can provide an auxiliary evaluation method for the safety factor method.